The present invention is concerned with a method and apparatus for accurately controlling various chemical and physical processes in which liquids are involved and in which it is desired to control the concentration and/or specific gravity of the liquids in the system. In such systems it is necessary to monitor variations in liquid compositions occasioned by the addition or removal of other liquids, concentration of dissolved constituents therein, etc. Typical of such operations are the manufacture of various beverages and liquid products, such as beer, soups, gasoline, milk and wine.
While it has been suggested in the past to use a hydrometer in a reservoir of sampled solution as a means of monitoring the operation of such processes, e.g. see U.S. Pat. No. 2,320,720, such systems have in general not found wide use due to the difficulty in obtaining accurate meaasurements and sensing small variations. The hydrometer itself often tends to stick in its position. Additionally, changes in flow rate, temperature and the like have not in the prior art systems been readily accommodated. Controlling accuracy within a very small degree has been unobtainable.